1,3,2-diazaphospholidines

With the C2 symmetry of the chiral diamine, no new stereogenic center is created at the phosphorus atom, thus avoiding the need for a sometimes difficult separation of diasteroisomers, such as with amino alcohols. 

The major diastereomer 95 could be obtained in optically pure form by silica gel chromatography. The absolute configuration of the amination product was dictated by the choice of the chiral diamine, and correlated with previous results in asymmetric a-alkylation. Furthermore, the major diastereomer 95 was converted to the corresponding (ft)-a-aminoethyl phosphonic acid 96 by sequential treatment with (i) TFA, CH2C12,0 °C (ii) 1 N HC1 and (iii) H2, Pt02,70 psi, followed by Dowex 50 (H+) resin chromatography in 73 % overall yield. Optical rotation of the a-amino phosphonic acid 96 allowed the confirmation of its optical purity ( 98 %) and of its absolute configuration. 

In the course of a study on electrophilic amination of achiral phosphonates, Maffre and co-workers described a single example starting from the same chiral phospho-namide 94, and obtained a 4 1 mixture of diastereomers 95 in 33 % yield [50], 

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A highly diastereoselective exchange reaction between a variety of bis(dimethy-lamino)arylphosphines and (S)-2-(anilinomethyl)pyrrolidine (197a) and its SV-aryl analogues constituted a key step in the synthesis of a series of substituted monodonor diazaphospholidine ligands, 213-220 [90, 91] (Figure 1). 

This methodology was applied successfully also for the diastereoselective synthesis of a series of P-stereogenic (o-hydroxyaryl)diazaphospholidine - borane complexes 250-257 (yields ranging from 40 to 86%) via the reaction sequence shown in Scheme 61 with a one-pot formation of the appropriate (o-bromoaryloxy) diazaphospholidine-borane complexes 242-249 in yields ranging from 70 to 92% (Scheme 61) [93],... 

A method for the preparation of 1,3,2-diazaphospholidine heterocydes has been described by Deng and Chen (Scheme 6.225) [402], The authors found that treating hindered 1,2-diamino substrates such as a-amino acid amides with tris(diethylami-no)phosphine as reagent/solvent under open-vessel microwave conditions at 250 °C for 1 min furnished a trivalent phosphorus intermediate. Subsequent thiation of this intermediate with elemental sulfur in refluxing benzene provided the target l,3,2-diazaphospholidin-4-ones in good overall yields. The yields were much improved compared to those achieved by standard thermal methods. 

Monodentate Phosphinites, Aminophosphinites, Diazaphospholidines and Secondary Phosphine Oxides... 

Scheme 28.13 Monodentate phosphinites, aminophosphinites, diazaphospholidines and secondary phosphine oxides.

The use of diazaphospholidines as chiral derivatizing agents for the determination of the enantiomeric composition of choro- or bromohydrins has been reported. Thus, 31P NMR spectra of a range of diastereomeric derivatives have been described to show a systematic deshielding from 0.2 to 12.9 ppm of isomers 48 compared to isomers 49 <2000TA1273>. 

Alkyl(aryl)phosphonites react with AW -disubstituted ureas and thioureas in the presence of aldehydes to give 1,2,4-diazaphospholidines (58) these compounds... 

Scheme 25). l-Oxo-2,8-diphenyl-2,5,8 triaza-1 X -phosphabicyclo[3.3.0]octane (68) formed by acid catalysis of the bicyclic phosphoric triamide (67) has been found to isomerize via a new type of rearrangement to yield the ring contracted 3-[2-(phenylamino)ethyl]-2-oxo-2-ethoxy-l-phenyl-l,3,2 A, -diazaphospholidine (69). The rearrangement has been explained in terms of intramolecular 1,5-nucleophilic attack... 

More powerful than the Anderson-Shapiro reagent is the diazaphospholidine reagent developed by Alexakis and co-workers37 39. The reagent is easily prepared by amine exchange of p[N(ch3)2]3 with (R,R) N,A -dimethylcyclohexane-l,2-diamine in refluxing toluene. It must be stored as an 0.2 M solution under nitrogen. The reaction with the analyte alcohol is run in the NMR tube at room temperature. 

Catalytic conversion of isocyanates into carbodiimides with the aid of l,3-dimethyl-l,3,2-diazaphospholidine 2-oxides and 1,3-dimethylhexahydro-1,3,2-diazaphosphorine 2-oxides [79]. 

ALKENES 1,3-Dimethyl-2-phenyl-l, 3,2-diazaphospholidine Iodine. Phenylthio(triphenylstannyl)methyllithium. Sodium amalgam. Sodium sulfide. Tri-n-butyltin hydride. Triethyl orthoformate. 

New P-stereogenic (o-hydroxyaryl)diazaphospholidines, in the form of their borane complexes (19), have been synthesized in a totally diastereoselective manner by a P-0 to P-C migration rearrangement of (o-bromoaryloxy)diazaphospholidine-borane complexes (18) mediated by r-BuLi (Scheme 5).16 The stereoselective rearrangement, confirmed by X-ray diffraction study of the structures of the product (21) and its precursor (20), occurs with clean retention of the phosphorus configuration. 

Various l,3,2-diazaphospholidin-4-thione-2-sulfides 91 were prepared in moderate yield by the reaction of 3-substituted glycinamides 89 with Lawesson s reagent 90 in benzene at 55-60°C (Equation 6) <1999HAC105, 1997PS(129)111>. A similar procedure based on the reaction of Lawesson s reagent 90 with a-aminonitriles was used for the synthesis of 1,3,2-diazaphospholidine-4-thione 2-sulfide derivative 92 <2001S2445>. 

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